I. Field
The following description relates generally to wireless communication systems and more particularly to handoff groups in a wireless communication network.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and other content. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) systems, orthogonal frequency division multiple access (OFDMA) systems, and so forth.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations through transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established through a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the Ns independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point.
To effectuate continued coverage for terminals, the access points (base stations, access networks, etc.) associated with cellular networks are geographically positioned so as users (and associated terminals) change location they do not lose services. Thus, mobile stations can be “handed off” from a first base station to a second base station. In other words, a terminal will be serviced by a first base station while in a geographic region associated with such base station. When the terminal is transported to a region associated with a second base station, the terminal will be handed off from the first base station to the second base station. With hard handoff, the link to the prior base station is terminated before or as the user (e.g., associated terminal) is transferred to the new base station. Ideally, the handoff occurs without data loss, loss of service, and the like.